The past few days, news reports have cropped up allovertheplace about the swarm of earthquakes that have recently occurred in Yellowstone National Park and the media is throwing around the term “supervolcano” like it’s going out of style.

In fact, many articles and discussions feature the following statistic: “The Yellowstone Caldera erupts every 600,000 years. The last eruptions was 640,000 years ago. That means we are over due!”

Whoa. That’s scary stuff! Especially when you see videos that talk about what would happen if it were to erupt.

How Often Do Eruptions Occur?

But how likely is it that Yellowstone is about to erupt?

We know that in the past few million years, Yellowstone has had three, large caldera forming eruptions: 2.1 million years ago, 1.3 million years ago, and 640,000 years ago.1

That gives us two data points to try and determine a recurrence interval: 800,000 years between eruptions and 660,000 years between eruptions. You can’t even do basic statistical analysis using only those two data points! About the only thing you can do is say that Yellowstone erupts, “on average, once every 730,000 years.”

What is Most Likely to Happen?

“Cool! So we’re safe!” you might think.

Mostly! That average is only for catastrophic eruptions that form calderas. We know the last eruption that occurred within the Yellowstone Caldera itself, was 70,000 years ago. This type of eruption resulted in large, rhyolitic lava flows. These types of flows aren’t usually violent, as the viscous lava would only move at most, a few hundred feet a day. These types of flows occurred erupted slowly, over time, and eventually filled the Yellowstone Caldera over a period of 90,000 years (beginning 160,000 years ago). 2

A great (though smaller) example of this type of lava flow is found here in Northern California, at Obsidian Dome.

This article from the American Museum of Natural History talks about what effects this type of eruption would have on the park:

â€œIf a lava flow were to occur here today, it certainly would have an effect,â€ says Lowenstern. â€œBut it wouldnâ€™t cause many, if any, deaths.â€ Lava is what magma is called after it breaches Earthâ€™s surface. About 80 lava flows since Yellowstoneâ€™s last big eruption 640,000 years ago have filled in much of the three calderas, so that their entire circumferences are only detectable with careful fieldwork. Lava erupting from existing or new cracks at Yellowstone would likely be thick and viscous and have little gas left in it. Thus, it would ooze, not explode, and be unable to flow long distances easily. â€œTourists just wouldnâ€™t be allowed in certain areas,â€ says Lowenstern.

The remaining molten rock in Yellowstoneâ€™s collapsed magma chamber is now cooling. It donates heat to the water table above it, which creates Yellowstoneâ€™s more than 10,000 hydrothermal features. The hot groundwater can flash as steam in geysers like Old Faithful or belch through cauldronlike mud pots. The water also collects in pools, some of which are acidic, near boiling, blue-green with minerals and microbes, and reeking of rotten-eggy hydrogen sulfide. (â€œThe smell of life,â€ Lowenstern calls it.) An unanticipated hydrothermal explosion could scald or severely injure park visitors and staff.

The Yellowstone Hotspot

The interesting thing about Yellowstone and the hotspot that currently sits beneath it, is that it has had a fairly active history. You can track remnants of previous calderas across Southern Idaho and into Oregon, evidence that the hot spot has remained in the same place while the North American slowly plate moves over it.

You can see in the graphic above that each caldera has dates associated with activity that occurred in those locations. Most of the activity in each location occurred over a span of 2 to 3 million years. And guess what? We’re currently at 2.1 million years since activity began in this current location!

Does that mean we have nothing to worry about? Maybe. But maybe not.

Should We Worry?

Based on what we do know about past eruptions, the chances of a supervolcano erupting in our lifetimes (or the lifetimes of your great great great great grandchildren) are slim. But we can’t predict the future. This is why it’s so fun to be a scientist. We get to try and figure this stuff out!

Honestly, just sit back and enjoy life. And remember, the next time you see something beautiful like this, just remember the powerful forces at work below your feet that have enabled its existence.